212 Evans: HEpATICAE OF PUERTO RICO 
The leaf-cells also exhibit considerable uniformity. The outer 
wall of each cell is usually more or less convex, making the sur- 
face of the leaf slightly roughened and approaching in this respect 
the genus Zrachylejeunea; but the convex wall is not thickened 
except sometimes on the marginal teeth. .Trigones and _inter- 
mediate thickenings, although varying greatly in size, can almost 
always be demonstrated (PLATE 10, FIGURE 21), Ocelli are absent 
from all the Puerto Rico species and it is doubtful if they occur 
anywhere in the genus. 
The lobule is built up on essentially the same principle as in 
Harpalejeunea and Cyclolejeunea. It has a strongly arched keel, 
more or less roughened throughout, and the free margin is tipped 
with a single curved cell (PLATE 10, FIGURE 24), which is normally 
appressed to the lobe and thus assists in forming the opening into 
the well-developed water-sac. The hyaline papilla is proximal in 
position, but the depression in which it is situated is very shallow 
or even entirely obsolete. The papilla itself is conspicuous and 
lies parallel with the free margin, very much as in Hygrolejeunea 
and Taxilejeunca. Sometimes a lobule is poorly developed and 
fails to show some of the characters just enumerated. 
The underleaves, which are very much like those of Zrachyle- 
jeunea, are usually small and distinct and vary in shape from 
broadly ovate to orbicular. They are deeply bifid with triangular 
lobes separated by a broad sinus. The rhizoids when present 
grow out from a definite patch of thin-walled cells at the base of 
the underleaf (PLATE II, FIGURE 9), and sometimes an extremely 
rudimentary disc is developed. The radicelliferous region is sep- 
arated from the base of the sinus by from one to three cells and is 
bounded on each side by a single large cell. The line of insertion is 
short and scarcely arched. The margin of the underleaf is usually 
entire or crenulate but is sometimes angular-dentate on the sides. 
In the majority of the species the inflorescence is autoicous 
but in a few it is dioicous. The female branch is extremely short 
and rarely bears more than a single rudimentary leaf and a single 
underleaf in addition to the involucre and perianth. Occasionally 
a single pair of normal leaves with their underleaf is interpolated 
between the rudimentary leaf and the bracts (PLATE 11, FIGURE 18), 
but this condition seems to be unusual and is limited to certait 
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